Elevations

Does anyone know of a good android application that can be used to give accurate elevations that i could use  to get the elevations of my data measurement points during calibration?

  • While cell phone GPS devices are all right for getting x,y coordinates, they are not very good for elevation for modeling. You'll always have issues with pressure calculations if you elevations are not accurate. You need to be talking about "sub-meter accuracy" for model elevation data. You need to find your local expert in GPS and hire them or rent their equipment. You can usually find this kind of equipment at a consulting company or university, or you can buy it yourself. Or you can extract elevation data from a high quality digital terrain model using Trex (terrain extraction) in WaterGEMS. But understand the accuracy of the DTM before you start.

  • One of the best sources of elevation data are LIDAR data sets. You may want to check with your local planning agency, federal government or sewer utility to see if they have any LIDAR data.

    Google Earth also is a source of elevation data if you just want a few points but I would want to verify the accuracy for your specific area.

  • I just looked up the Root Mean Square Error for Google Earth elevation data and it is only 6.213 m, which I would not consider to be accurate enough for modeling, except for very rough checking in hilly areas.

  • And I am considering whether or not I should use fire hydrant test for calibration or if I can simply collect field data during peak hours. From what I understand this would be dependent on the amount of velocity of the water traveling within the pipes. So my question is at what velocity's can the modeler be assured that they would be capturing the impact of ,pipe roughness, closed valves and demand errors to a significant degree. Because if  the velocity in my system is reaching that velocity during peak hours I could simply set out a bunch of pressure and flow loggers during peak hour and calibrate based on that instead of having to conduct a bunch of fire flow tests.